The invention relates to the use in a composition for caring for human hair or eyelashes of an effective amount of a pyridinedicarboxylic acid derivative of general formula (I) or of one of its salts, ##STR00001## in which R.sub.1 and R.sub.2 represent, independently of one another, OH, OR', --NH.sub.2, --NHR' or --NR'R'', and R' and R'' represent, independently of one another, a saturated or unsaturated and linear or branched C.sub.1-C.sub.18 alkyl radical or an aryl radical, this alkyl or aryl radical optionally being substituted by at least one OH, alkoxy, acyloxy, amino or alkylamino group, or R' and R'' together represent a heterocycle, the composition being intended to induce and/or stimulate the growth of human keratinous fibers, such as the hair and eyelashes, and/or slow down their loss; the invention also relates to a cosmetic treatment intended to stimulate the growth of human keratinous fibers, such as the hair and eyelashes, and/or slow down their loss.